Dental material comprising adducts of 3-methacroyl-2-hydroxypropyl esters with diisocyanates

ABSTRACT

Dental materials containing dimethacrylates having the following chemical structures: ##STR1## where R 1  and R 2  may be the same or different and are cyclohexyl or phenyl groups which may be substituted or unsubstituted; and 
     R 3  is an aliphatic cycloaliphatic or aromatic group having 6 to 15 carbon atoms.

CROSS REFERENCE TO OTHER CASES

This is a division of application Ser. No. 267,608, filed May 27, 1981,now U.S. Pat. No. 4,400,159 which is a CIP of Ser. No. 162,482, filedJune 24, 1980.

BACKGROUND OF THE INVENTION

The present invention relates to a polymerizable compound, a polymerformed from this compound, a dental material containing this compound, amethod for polymerizing this compound in situ on teeth, and a toothcomprising a polymer of this compound.

In recent years, the use of polymer-based dental materials became veryprominent as they improved aesthetics and durability of restorations,faciliated application techniques and allowed great expansion of dentaltechniques in restorative, corrective and preventive applications.Especially important became filled restorative materials, cements,bonding agents, fissure sealers and orthodontic adhesives based on thepolymerizable in situ aromatic and aliphatic methacrylates. The bestproperties in these materials have been obtained when the resin part ofthe composition is comprised of one or more of the following monomers:##STR2## i.e., 2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane(known in the industry as Bis-GMA), its adducts with variousalkyl-isocyanates, such as adducts described in the Waller U.S. Pat. No.3,629,187, the entire disclosure of which is hereby incorporated byreference and relied upon, and ##STR3## i.e.,2,2-bis[4'(2"-methacroylethoxy)phenyl]propane (known in the industry asEBA).

These high molecular weight monomers are usually diluted with lowermolecular weight polymethacrylates including dimethacrylates such asdi-, tri- or tetraethylene glycol dimethacrylate, 1,6-hexanedioldimethacrylate, or trimethacrylates such as trimethylolpropanetrimethacrylate. Other methacrylate monomers known to be used in certainrestorative materials, cements, fissure sealers, bonding agents ororthodontic adhesives and claimed to improve mechanical, physical,clinical or aesthetic properties of materials are: ##STR4## i.e.,2-methacroylethyl-3-methacroyl-2-hydroxypropyl tetrahydro (or hexahydro)phthalate and ##STR5## i.e., 2,2 bis-(4'-methacroylphenyl)propane (knownin the industry as BADM).

In an attempt to improve methacrylate resin based dental materials,research efforts have been concentrated mainly on reducing their watersorption, as related to susceptibility to hydrolysis and staining, onminimizing their polymerization shrinkage and on improving theirresistance to discoloration when exposed to sunlight.

These properties depend on the chemical structure of the monomer ormonomers used in the formulation and their purity. In the formulationscontaining (besides the resin binder) a solid phase in the form ofdispersed filler particles, the viscosity of the resin constitutesanother important factor. The lower the viscosity of the alternativemonomers that may be used in the formulation, other properties remainingsimilar or the same, the more filler may be incorporated in theformulation contributing to lower shrinkage, lower water sorption,better wear resistance and overall improved mechanical properties.

As it is recognized in the dental profession, the composite restorativesknown up to now were unsuitable in most instances for use in posteriorrestorations, mainly because of their unsatisfactory wear resistance.This is especially true for Class II restorations as exposed the most tostrong mastication forces. The typical properties of compositerestoratives made according to presently known techniques are givenbelow:

    ______________________________________                                        Water Sorption as 37° C.                                                                0.7 mg/cm.sup.2                                              Compressive Strength                                                                           30,000-40,000 psi                                            Diametral Tensile Strength                                                                     3,480-4,600 psi*                                             Color Stability  Discoloration perceptible with                                                difficulty                                                   Hardness (Barcol)                                                                              98                                                           Opacity/Translucency                                                                           0.35-0.55*                                                   Filler/Resin ratio by Weight                                                                   3.2:1 to 4.2:1                                               ______________________________________                                         *Determined according to American Dental Associtaion Specification No. 27     JADA, Vol. 94, June, 1977.                                               

In addition to the above-mentioned Waller U.S. Pat. No. 3,629,187,various polymeric dental materials have been described in the followingU.S. Pat. Nos. 3,066,112 (Bowen); 3,179,623 (Bowen); 3,194,783 (Bowen);3,194,784 (Bowen); 3,539,533 (Lee II et al.); 3,541,068 (Taylor);3,597,389 (Taylor); 3,721,644 (Stoffey et al.); 3,730,947 (Stoffey etal.); 3,751,399 (Lee, Jr. et al.); 3,766,132 (Lee, Jr. et al.);3,774,305 (Stoffey et al.); 3,860,556 (Taylor); 3,862,920 (Foster, etal.); 3,926,906 (Lee, II et al.); 4,102,856 (Lee, Jr.); and 4,107,845(Lee, Jr. et al.). Further information on polymer based dental materialsis given on pages 501-508 and 515-517 of the Kirk-Othmer Encyclopedia ofChemical Technology, Third Edition, Volume 7 (1979). The entiredisclosures of the patents and the Kirk-Othmer reference set forth inthis paragraph are hereby incorporated by reference and relied upon.

An important improvement in clinical performance of polymer-based dentalrestoratives may be achieved and their scope of applications greatlyexpanded if their water sorption is lowered, mechanical strength andhardness improved and filler/resin ratio significantly raised.Accordingly, there is a need in the art to develop polymerizablecompounds which tend to overcome the shortcomings of the prior artpolymerizable compounds used in dental materials.

SUMMARY OF THE INVENTION

The present invention relates to a compound of the following formula:##STR6## where

R₁ and R₂ may be the same or different and are cyclohexyl or phenylgroups which may be substituted or unsubstituted; and

R₃ is an aliphatic cycloaliphatic or aromatic group having 6 to 14carbon atoms.

Other aspects of this invention relate to a polymer formed from thiscompound, a dental material (e.g., particularly a composite restorativematerial) containing this compound, a method for polymerizing thiscompound in situ on teeth and a tooth comprising a polymer of thiscompound.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a dimethacrylate compound represented by thestructure: ##STR7## where

R₁ and R₂ may be the same or different and are cyclohexyl or phenylgroups which may be substituted or unsubstituted; and

R₃ is an aliphatic, cycloaliphatic or aromatic group having 6 to 14carbon atoms.

Dimethacrylate compounds of this formula are referred to herein ascompounds of the present invention. It will further be understood thatstructures given herein are intended to connote all possiblestereoisomers and combinations thereof.

Although not intending to be strictly limited to any particular meansfor forming the compounds of the present invention, it is noted thatthese compounds may be described as adducts of3-methacroyl-2-hydroxypropyl esters with diisocyanates. Thus, forexample, an acetic acid derivative of the formula R₄ --CH₂ --COOH, whereR₄ is R₁ or R₂, may be reacted with glycidyl methacrylate to form ahydroxy-containing ester intermediate of the formula: ##STR8## Moreparticularly, the acetic acid derivative used to form this esterintermediate may be represented by the formula ##STR9## where ##STR10##is a cyclohexyl or phenyl ring; and

R₅, R₆ and R₇ may be the same or different and are preferably eachhydrogen, but may also be alkyl or alkoxy groups having up to 12 carbonatoms. Such alkoxy groups may be represented by the formula --OR₈, whereR₈ is an alkyl group as defined for R₅, R₆ and R₇, e.g., having up to 12carbon atoms. Preferably, these R₅, R₆, R₇ and R₈ groups have up to 4carbon atoms. Examples of R₅, R₆, R₇ and R₈ include methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, tert. butyl, straight orbranched chain pentyl, straight or branched chain hexyl, straight orbranched chain heptyl, straight or branched chain octyl, straight orbranched chain nonyl, straight or branched decyl, straight or branchedchain undecyl and straight or branched chain dodecyl. The groups R₅, R₆and R₇ may be substituted in any possible position on the cyclohexyl orphenyl ring.

One or more of the above-mentioned hydroxy-containing esterintermediates may then be reacted with one or more diisocyanates of theformula

    O═C═N--R.sub.3 --N═C═O

where R₃ is defined as above, to form compounds of the presentinvention. Examples of such diisocyanates include hexamethylenediisocyanate, octamethylene diisocyanate, decamethylene diisocyanate,undecamethylene diisocyanate, dodecamethylene diisocyanate,xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, m-phenylenediisocyanate, p-phenylene diisocyanate, toluene-2,6-diisocyanate,mesitylene diisocyanate, durylene diisocyanate, benzidene diisocyanate,1-methyl phenylene-2,4-diisocyanate, naphthylene-1,4-diisocyanate,naphthylene-1,5-diisocyanate, 3,3'-dimethyl-4,4'-diisocyanato diphenylmethane, 4,4'-diphenyl propane diisocyanate, dianisidine diisocyanate,cyclohexamethylene-1,4-diisocyanate, cyclohexamethylene-1,3-diisocyanateand 4,4'-diisocyanato dicyclohexyl methane. Preferred diisocyanatesinclude hexamethylene diisocyanate and 4,4'-diisocyanato dicyclohexylmethane.

As mentioned previously an hydroxy-containing ester intermediate may beformed by reacting one or more compounds of the formula R₄ --CH₂ --COOHwith glycidyl methacrylate. This reaction may take place in the presenceof a suitable electron donating catalyst such as triphenylphosphine anda polymerization inhibitor such as butylated hydroxytoluene (BHT). Afterremoving excess glycidyl methacrylate from this reaction mixture, one ormore diisocyanates may be added thereto to form one or more compounds ofthe present invention. Accordingly, compounds of the present inventionmay comprise various single compounds or mixtures of compounds.Preferred compounds of the present invention include adducts ofphenylacetic acid/glycidyl methacrylate intermediates with4,4'-diisocyanato dicyclohexyl methane or hexamethylene diisocyanate.

The dimethacrylates of the present invention may be combined with otherpolymerizable unsaturated materials, such as acrylic or methacrylicmonomers or prepolymers, and polymerized. Thus, the dimethacrylates ofthe present invention may be polymerized to form either homopolymers orcopolymers, e.g., containing at least 10% by weight of thesedimethacrylate moieties. Preferably, copolymers of the dimethacrylatesof the present invention may contain at least 40% by weight of thesedimethacrylate moieties. As used herein, the term "moiety" shall connotean entire repeating polymeric unit and not some lesser fragment thereof.

Polymers of the dimethacrylates of the present invention arecharacterized in that they may have a high degree of crosslinking.Accordingly, these dimethacrylates may be added to mono-functionalacrylic and methacrylic monomers and polymerized to form cross-linkedpolymers. Examples of these acrylic and methacrylic compounds includeacrylic and methacrylic acid and esters thereof with alcoholscontaining, e.g., 1 to 4 carbon atoms. Examples of such acrylic andmethacrylic esters include methylmethacrylate, ethylmethacrylate,butylmethacrylate, methylacrylate, ethylacrylate and butylacrylate.

Copolymers having an even higher degree of cross-linking may be producedby copolymerizing the dimethacrylates of the present invention withother polyfunctional acrylic ester or methacrylic ester monomers, i.e.,monomers containing two or more acrylic or methacrylic functionalities.One class of these polyfunctional monomers includes monomers which areused as diluents in dental materials. Such polyfunctional acrylic esteror methacrylic ester monomers include alkylene glycol diacrylates,alkylene glycol dimethacrylates, polyalkylene glycol diacrylates,polyalkylene glycol dimethacrylates, alkanetriol triacrylates andalkanetriol trimethacrylates, e.g., containing from 8 to 18 carbonatoms. Examples of such monomers include ethylene glycol dimethacrylate,di-, tri- or tetraethylene glycol dimethacrylate, 1,6-hexanedioldimethacrylate, the dimethacrylate formed by the reaction of methacrylicacid with butanediol, trimethylolpropane trimethacrylate and the acrylicesters corresponding to these methacrylates, e.g. ethylene glycoldiacrylate. As far as polyfunctional acrylates and methacrylates areconcerned, these monomers are characterized by relatively low molecularweight (e.g., 339 or less) and low viscosity. The above-mentionedpolyglycol dimethacrylates are further characterized by low surfacetension.

Another class of polyfunctional acrylates and methacrylates includes therelatively high molecular weight (e.g., 364 or more) acrylic ormethacrylic monomers used in dental compositions. Such polyfunctionalcompounds include, especially, dimethacrylates such as2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane (i.e.Bis-GMA), 2,2-bis[4'(2"-methacroylethoxy)phenyl]propane (i.e., EBA),2-methacroylethyl-3-methacroyl-2-hydroxypropyl tetrahydrophthalate,2-methacroylethyl-3-methacroyl-2-hydroxypropyl hexahydrophthalate and2,2-bis(4'-methacroylphenyl)propane (i.e. BADM). Further polyfunctionalmonomers containing up to four acrylic or methacrylic functionalitiesare described in the Stoffey et al. U.S. Pat. No. 3,721,644, the entiredisclosure of which is hereby incorporated by reference and relied upon.

Accordingly, copolymers may be formed from polymerizable materialscomprising at least one dimethacrylate of the present invention and,e.g., at least 10% by weight of one or more of the copolymerizablematerials described herein.

Polymerization of the dimethacrylates of the present invention may beinitiated by known means for initiating the polymerization ofdimethacrylates such as heat, chemical means orelectromagnetic-irradiation. Thus, in order to induce curing ofdimethacrylates, a free-radical catalyst may be incorporated therein.Organic peroxide initiators, such as methyl ethyl ketone peroxide,t-butyl peroctoate, iso-propyl percarbonate, cumene hydroperoxide,dicumyl peroxide, and especially benzoyl peroxide, are preferred.

The ability of the initiator to cure dimethacrylates may be enhancedthrough the use of activators or accelerators. Thus, a peroxideinitiator can be activated with a tertiary aromatic amine such asN,N-dimethyl-p-toluidine or N,N-bis(2-hydroxyethyl)-p-toluidine.

The amount of free-radical catalyst may be selected according to thecuring rate desired. For instance, if a relatively slow curing rate isdesired, a minimum catalytically effective amount, such as 0.5% byweight based on the polymerizable components, may be selected. On theother hand, when faster rates of cure are desired, greater amounts offree-radical catalyst, such as 4.0% or more by weight based on thepolymerizable components, may be selected. Accordingly, the amount ofcatalyst may range from about 0.5 to about 4.0% by weight based upon theweight of the polymerizable components.

As with the free-radical catalyst, the amount of the activator selectedmay vary, e.g., from about 0.5 to about 4.0% by weight of thepolymerizable components, depending upon the desired curing rate.

Polymerization of the dimethacrylates of the present invention may alsobe initiated by ultraviolet or visible light using known light activatedpolymerization initiators such as benzoin, benzoin methyl ether, benziland other commercially available photoinitiators. For example, one mayselect from about 1% to about 5% by weight based on the polymerizablecomponents of a sensitizer capable of initiating polymerization whenexposed to UV light between about 3550 A. to about 3720 A.

The various components of a material containing a dimethacrylate of thepresent invention may be combined in any suitable manner. However, sincechemically initiated polymerization starts immediately upon admixture ofall three of (1) a methacrylate, (2) an initiator and (3) an activator,it is necessary to separate at least one of these components from theothers until immediately before polymerization of the methacrylate. Thisseparation may be achieved through the use of a two-package product,wherein various components of a material containing a dimethacrylate ofthe present invention are separately contained until the time ofpolymerization.

Therefore, the components of such a composition may be separated bymeans of a two-package product into two parts, one part containing thepolymerization initiator and the other part containing thepolymerization accelerator.

It is helpful to package polymerizable methacrylates with inhibitors,such as butylated hydroxytoluene (BHT) or hydroquinone methyl ether.Thus, BHT may be included in an amount from about 0.1 to about 0.3% byweight based on the polymerizable components to increase the storagestability of these polymerizable components.

Ultraviolet stabilizers such as 2-hydroxy-4-methoxybenzophenone (CyasorbUV-9, a tradename of American Cyanamide) may be included to enhance thestability of the polymerizable components as well as polymers resultingtherefrom. For example, from about 0.4 to about 1.6% by weight ofCyasorb UV-9 based on the weight of the polymerizable components may beused for this purpose.

In addition to polymerizable unsaturated material, inorganic orpolymeric fillers may also be added to the monomers of the presentinvention prior to polymerization of these monomers. Accordingly, theterm "polymer" as used herein may connote a polymeric matrix materialwhich binds together various fillers.

Up to about 6.5 parts or even up to 8.5 parts of filler material perpart of polymerizable unsaturated material may be included. Particularinorganic filler materials include silica materials (e.g., powderedquartz, barium glasses, borosilicate glasses, SiO₂, fumed silica andlithium aluminum silicate) and alumina materials (e.g., Al₂ O₃). Theseinorganic filler materials may be treated with coupling agents, such as[3-(methacroyl)propyl]trimethoxysilane, in order to assure the properincorporation of filler into the polymeric matrix of the cured product.Other materials such as pigments may also be included in polymerizablematerials comprising the dimethacrylates of the present invention.

It is noted that by varying the nature and proportions of curablecompositions comprising one or more dimethacrylates of the presentinvention, a variety of such curable compositions as well as a varietyof cured compositions resulting therefrom may be obtained. For example,curable compositions containing a relatively large amount of fillers,and relatively small amounts of low viscosity acrylic or methacrylicdiluents, as well as minimum amounts catalysts and activators, may havea thick, doughlike consistency and a slow curing rate permitting workingof the composition by molding and shaping before setting occurs. On theother hand, compositions containing little or no filler and relativelylarge amounts of low viscosity diluents, catalysts and accelerators maybe flowable and fast curing, permitting brush-on application wherelittle or no molding or shaping is required.

Polymerizable materials containing dimethacrylates of the presentinvention may now be described by way of examples of various dentalmaterials. In this regard, composite restorative materials are givenparticular emphasis.

COMPOSITE RESTORATIVE MATERIALS

Composite restorative material, as the name implies, is a compositematerial of a polymerizable material and a suitable filler. Thesematerials are capable of curing in situ on teeth to restore a hardenedsurface thereto. These materials are generally applied as a fillingmaterial to prepared or drilled teeth. Accordingly, compositerestorative materials should be of a thick, workable consistencysuitable for application to a prepared tooth and capable of being shapedor molded thereon before setting occurs. Thus, composite restorativematerials are relatively slow curing.

The thick consistency of composite restorative materials, as well as thedesirable properties of the cured product formed from these materials,are largely a function of the relatively large amounts of fillermaterials employed therein. More particularly, composite restorativematerials may contain glass or ceramic fillers in excess of thepolymerizable material employed therein.

When the polymerizable material of the composite restorative containsone or more dimethacrylate monomers of the present invention, the weightratio of filler to polymerizable material may range from about 1.5:1 toabout 6.5:1 or even up to about 8.5:1 and, most especially, from about4:1 to about 6:1. Suitable ceramic or glass fillers include silicamaterials, such as powdered quartz, barium glasses, borosilicateglasses, SiO₂ and lithium aluminum silicate, and alumina materials, suchas Al₂ O₃. Since composite restorative materials must be capable ofconforming to the confined space of prepared tooth and hardening thereinto achieve restorative properties, the particle size of these fillersmust be sufficiently small. Generally, the particle sizes of thesefillers may range from about 1 to about 150 microns, preferably fromabout 1 to about 40 microns. The average particle size of these fillersis preferably less than about 25 microns. Suitably, compositerestorative materials may contain a mixture of two or more fillers, suchas a mixture of a ceramic filler (e.g. powdered quartz) and glass filler(e.g., powdered glass).

According to techniques well known in the art, the fillers of compositerestorative materials may be treated with one or more organosilanecoupling agents. These coupling agents are also sometimes referred to asfinishing or keying agents and include materials such as[3-(methacroyl)propyl]trimethoxysilane. A sufficient coupling amount ofsuch coupling agent may be a small amount such as from about 0.5 toabout 1.0 part of coupling agent per 100 parts of filler. Methods fortreating fillers with coupling agents are described, for example, inU.S. Pat. No. 3,066,112 (Bowen), wherein an aqueous solution oftris(2-methoxyethoxy)vinyl silane is catalyzed with sodium hydroxide togive a pH of 9.3 to 9.8, and the filler is treated with this solution,for example, one-half percent of silane per weight of fused quartz. Aslurry so formed is dried at about 125° C. and cooled. Another techniquefor treating filler with a coupling agent is described in the passageextending from column 3, line 40 to column 4, line 4 of U.S. Pat. No.3,862,920 (Foster et al).

As indicated previously, the filler, rather than polymerizable material,constitutes a major portion of the composite restorative material.Perhaps for this reason the polymerizable material in compositerestoratives is sometimes referred to as a "binder".

The polymerizable materials for forming a composite restorative materialmay contain at least two monomeric components, termed herein a firstmonomer and a second monomer. This first monomer is at least onedimethacrylate monomer according to the present invention, and thesecond monomer is at least one relatively low molecular weight diluentmonomer which, among other purposes, serves to reduce the overallviscosity of the composite restorative materials.

The first monomer of the polymerizable material may be present in anamount of from about 20 to about 90% by weight, preferably from about 70to about 80% by weight, of the polymerizable material. The secondmonomer may be present in an amount from about 10 to about 80%,preferably from about 20 to about 30% by weight, of the polymerizablematerial.

As a second monomer, an acrylic or methacrylic diluent, which is usedfor this purpose in dental materials, may be selected. Moreparticularly, this diluent may be a di- or trimethacrylate having from10 to 18 carbon atoms. Diluents falling within this class of compoundsinclude relatively low molecular weight (e.g., 339 or less) alkyleneglycol dimethacrylates, polyalkylene glycol dimethacrylates andalkanetriol trimethacrylates. Particular examples of such diluentsinclude di-, tri- or tetraethylene glycol dimethacrylate, 1,6-hexanedioldimethacrylate, and trimethylolpropane trimethacrylate. Triethyleneglycol dimethacrylate is a preferred diluent.

The polymerizable material of composite restoratives may also contain atleast one third monomer. This third monomer may be a relatively highmolecular weight (e.g., 364 or more) polyfunctional acrylic ormethacrylic monomer used in dental compositions. Such polyfunctionalcompounds include dimethacrylates such as2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane (i.e.Bis-GMA), 2,2-bis[4'(2"-methacroylethoxy)phenyl]propane (i.e., EBA),2-methacroylethyl-3-methoacroyl-2-hydroxypropyl tetrahydrophthalate,2-methacroylethyl-3-methacroyl-2-hydroxypropyl hexahydrophthalate and2,2-bis(4'-methacroylphenyl)propane (i.e. BADM).

Although the third monomer constitutes a different class of materialsthan the first monomer, the first monomer and third monomer servesimilar functions. Therefore, the third monomer may be used as areplacement for a portion of the first monomer, provided that thepolymerizable material contains at least 20% by weight of the firstmonomer. This third monomer may be used in quantities close to thequantities of first monomer. For example, the weight ratio of the firstmonomer to the third monomer may range from about 3:5 to about 5:3.Accordingly, when the first monomer is present in an amount ranging fromabout 30 to about 50% by weight of the polymerizable material, the thirdmonomer may also be present in an amount ranging from about 30 to about50% by weight of the polymerizable material. Preferably, however, theweight percent of the first monomer is greater or equal to the weightpercent of the third monomer.

In describing various composite restorative compositions, mention hasbeen made of various specific compounds, such as triethylene glycoltrimethacrylate and Bis-GMA, which fall into classes of compoundsreferred to as a second monomer or third monomer. However, it will beunderstood that the polymerizable material of the composite restorativematerial may contain further compounds which may fall within thesecategories of second or third monomers and/or may even fall in someseparate and distinct category. For example, the polymerizable materialmay contain a small amount of methacrylic acid. However, due to theobjectionable odor and properties of methacrylic acid, this monomershould not be present in quantities in excess of about 2% by weight(e.g., between about 1 and 2% by weight of the polymerizable material).

Composite restorative compositions may be cured by any suitable means, achemically initiated system being preferred. This initiating systeminvolves the use of a catalyst and an accelerator. Peroxide catalystssuch as benzoyl peroxide and tertiary amine accelerators such asN,N-bis(2-hydroxyethyl)-p-toluidine are preferred. The amounts ofcatalyst and accelerator may each be from about 0.5 to about 2.0% byweight of the polymerizable materials.

Desirably, initial curing of the composite restorative material shouldtake place in about 1 to about 2 minutes upon admixture of thecomponents thereof in order to permit adequate mixing and manipulationof these components outside the mouth prior to application to a preparedtooth. However, final curing is desirably delayed for 4 to 6 minutesfrom the initial contacting of restorative components in order to permitproper molding and shaping inside the mouth. It is noted that templatestructures are sometimes used in this molding process. Compositerestorative materials having such curing characteristics may enable adentist to perform a complete restoration of a prepared tooth withinabout ten minutes, including grinding and polishing the restorativematerial after final setting.

Composite restorative materials may be packaged in any suitable manner.Preferably, a two-package system is used wherein each package containsfiller and polymerizable material in roughly equal amounts, one packagecontaining the catalyst and the other package containing theaccelerator. However, other systems are also possible. For example,according to another two-package system, one package may contain bothfiller and catalyst and the other package may contain polymerizablematerial and accelerator. Another system involves packaging togethereach of the components excluding the catalyst component. When thissystem is used, polymerization can be initiated by introducing catalystdropwise from a stock solution thereof. Such a stock solution isdescribed in the Taylor U.S. Pat. No. 3,541,068 (Note particularlycolumn 6, lines 23-50).

Whatever packaging system is used, it is helpful to packagepolymerizable materials with one or more polymerization inhibitors suchas BHT in order to enhance storage life. Also, shelf life of componentscontaining accelerators may be improved by removing traces of peroxidesfrom these components with a reducing agent.

Cured composite restoratives containing at least one monomer accordingto the present invention have desirable properties and may be capable ofholding up under strong mastication forces. For instance, thesematerials may have a water sorption at 37° C. of less than 0.5 mg/cm²(preferably 0.44 mg/cm² or less), a compressive strength of 40,000 psior more; a diametral tensile strength of greater than 5,000 psi(preferably 5,300 psi or more), a hardness (Barcol) of greater than 98(preferably 100 or more), and a linear shrinkage of 0.4% or less.

While particular emphasis has been devoted herein to the use of themonomers of the present invention in composite restorative materials, itwill be understood that these monomers may also be used in other dentalmaterials. Examples of these other dental materials are given in theWaller U.S. Pat. No. 3,629,187 (Note particularly column 11, line 26 tocolumn 15, line 36) and in the Kirk-Othmer Encyclopedia of ChemicalTechnology, Third Edition, Volume 7 (1979), pages 501-508 and 515-517.Waller characterizes these materials as, e.g., dental cements, dentalcavity liners and dental lacquers. Kirk-Othmer characterizes thesematerials as, e.g., unfilled tooth-restorative resins, pit and fissuresealants and adhesives.

In addition to one or more monomers according to the present invention,dental materials may contain one or more of the copolymerizablematerials described herein, provided that such copolymerizable materialis acceptable for oral application associated with dental treatment.Particular examples of such copolymerizable material include thosemethacrylate monomers mentioned herein with respect to compositerestorative materials. The fillers described herein with respect tocomposite restorative materials may also be used in certain other dentalmaterials.

Certain dental materials may contain various amounts of filler, whileother dental materials contain no filler at all. For instance, thedental cements described in the Waller U.S. Pat. No. 3,629,187 maycontain little or no filler if a transparent cement is desired, butthese cements may contain up to about a 1:1 ratio of filler topolymerizable material if a translucent cement is acceptable. It isnoted that fillers used in dental cements generally have smallerparticle sizes (e.g., an average particle size of 10 microns or less)with respect to fillers used in composite restorative materials.

Dental materials may be cured by a photoinitiation technique using knownlight polymerization initiators or by chemically initiated systemsincluding those systems using sulfinic acid activators.

In addition to fillers and polymerizable material, dental materials maycontain other substances. For instance, pigments may be included. Also,ultraviolet absorbers or stabilizers may be included to lessendiscoloration of the cured material. Furthermore, fluorides,bacteriostatic agents and antibiotics may also be included.

Dental materials may be applied to teeth in a variety of mannersdepending upon the nature of the material and the desired use. Forinstance, thick, slow-curing materials, such as composite restoratives,may be molded and shaped in the mouth before final curing takes place.On the other hand, flowable, fast-curing materials, such as cavityliners may be simply brushed on the surface of the treated tooth.

Dental materials such as restoratives, sealers, bonding agents, cementsand orthodontic adhesives containing in their resin part 20-90% of thedimethylacrylate of the present invention exhibit most desirableproperties, especially in respect to color stability, low watersorption, high mechanical strength and low polymerization shrinkage.

The following examples describe certain embodiments of the invention. Itis to be understood that these examples are given only to illustrate thenature of the invention and should not, in any way, be understood aslimiting the scope of this invention, defined in the claims.

EXAMPLE 1

330 g of glycidyl methacrylate (2.33 mole) and 272 g of phenylaceticacid (2 mole) were reacted at 100°-110° C. in the presence oftriphenylphosphine catalyst and BHT inhibitor for 16 hours. The excessof glydicyl methacrylate was then removed in a stream of dry air and thereaction mixture cooled to 45° C.

256 g (0.97 mole) of 4,4'-diisocyanato dicyclohexyl methane has beenintroduced over 6 minutes while maintaining the temperature at 45°-50°C. The reaction mixture was then left for 72 hours at room temperature.The reaction product constituted a yellow viscous liquid. It is referredto hereafter as PAMC.

EXAMPLE 2

To 371 g (1.33 mole) of an adduct of glycidyl methacrylate andphenylacetic acid was obtained as described in Example 1. 109 g (0.65mole) of hexamethylene diisocyanate was introduced over a one-hourperiod while maintaining the reaction temperature at the level of45°-55° C. The mix was then allowed to stand at room temperature for 72hours. The reaction product had a refractive index n_(D) ²⁵ 1.492 andconstituted a light yellow medium viscosity liquid. It is referred tohereafter as PAHD.

EXAMPLE 3

A dental composite restorative for use as a filling material in anteriorand posterior restorations has been formulated as follows:

    ______________________________________                                        Part A                                                                        (Parts by                   Part B                                            Weight)                     (Parts by Weight)                                 ______________________________________                                        70     PAMC                 70.9                                              12     Hexanediol dimethacrylate                                                                          12                                                13     Triethyleneglycol    13                                                       dimethacrylate                                                         0.9    Cyasorb UV-9         0                                                 0.1    BHT                  0.1                                               4      N,N--bis(2'hydroxyethyl-                                                                           0                                                        p-toluidine)                                                           0      Benzoyl peroxide     4                                                 200    Powdered quartz below 44                                                                           200                                                      microns, treated with metha-                                                  croylpropyl trihydroxysilane                                           300    2:1 mixture of powdered barium                                                                     300                                                      and borosilicate glasses                                                      below 44 microns, treated with                                                methacroylpropyl trihydroxysilane                                      ______________________________________                                    

Parts A and B when mixed in equal amounts cured in 120 seconds. Theresulting material had the following characteristics.

    ______________________________________                                        Water Sorption at 37° C.                                                                    0.44 mg/cm.sup.2 *                                       Diametral Tensile Strength                                                                         5,300 psi*                                               Compressive Strength 40,000 psi                                               Hardness (Barcol)    100                                                      Color Stability      Change perceptible                                                            with difficulty*                                         Opacity/translucency 0.45*                                                    factor (.sup.C 0.70)                                                          Linear Shrinkage     0.4%                                                     ______________________________________                                         *Determined according to method described in American Dental Association      Specification No. 27, JADA Vol. 94, June, 1977                           

EXAMPLE 4

A dental composite restorative for use as filling material in anteriorand posterior restorations has been formulated as follows:

    ______________________________________                                        Part A                      Part B                                            (Parts by Weight)           (Parts by Weight)                                 ______________________________________                                        75         PAHD             75.5                                              20         Triethyleneglycol                                                                              20.9                                                         dimethacrylate                                                     0.9        Cyasorb UV-9     0                                                 0.1        BHT              0.1                                               4          N,N--bis(2-hydroxyethyl)                                                                       0                                                            toluidine                                                          0          Benzoyl Peroxide 3.5                                               560        Powdered quartz below 44                                                                       500                                                          microns treated with                                                          methacroylpropyl trihy-                                                       droxysilane                                                        ______________________________________                                    

Parts A and B when mixed in equal amounts cured in 120 seconds.

The properties of the curing material were virtually identical to thosedescribed in Example 3.

While the use of the monomers of the present invention has beendescribed primarily with respect to dental materials, particularlycomposite restorative materials, it is noted that these monomers mayalso be used in other materials such as bone cements and UV curableinks. Thus, while certain representative embodiments and details havebeen shown for the purpose of illustrating the invention, it will beapparent to those skilled in the art that various changes andmodifications may be made therein without departing from the spirit orscope of the invention. It will be further understood that the inventionmay comprise, consist essentially of or consist of the steps ormaterials recited herein.

What is claimed is:
 1. A dental material comprising polymerizableunsaturated material comprising at least about 10% by weight of, adimethacrylate of the following chemical structure: ##STR11## where R₁and R₂ may be the same or different and are cyclohexyl or phenyl groupswhich may be substituted or unsaturated; and R₃ is an aliphatic,cycloaliphatic or aromatic group having 6 to 15 carbon atoms, theremainder of said polymerizable material being at least 10% by weight ofat least one acrylic or a second and different methacrylic monomeracceptable for oral application associated with dental treatment.
 2. Adental material according to claim 1, wherein said polymerizableunsaturated material comprises about 20 to about 90% by weight of saiddimethacrylate and about 10 to about 80% by weight of at least one otherpolymethacrylate suitable for use in dental materials.
 3. A dentalmaterial according to claim 2, wherein said other polymethacrylate isselected from the group consisting of diethylene glycol dimethacrylate,triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate,1,6-hexanediol dimethacrylate, trimethylolpropane trimethacrylate,2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane,2,2-bis[4'(2"-methacroylethoxy)phenyl]propane,2-methacroylethyl-3-methacroyl-2-hydroxypropyl tetrahydrophthalate,2-methacroylethyl-3-methacroyl-2-hydroxypropyl hexahydrophthalate and2,2 bis-(4'-methacroylphenyl)propane.
 4. A dental material according toclaim 1 comprising two parts capable of curing upon mixing of theseparts, one of said parts comprising a peroxide-type polymerizationinitator and the other of said parts comprising a tertiary aromaticamine-type activator.
 5. A dental material according to claim 1comprising a light activated polymerization initiator capable of curingsaid dental material upon irradiation with ultraviolet or visible light.6. A composite restorative material comprising glass or ceramic fillerand polymerizable material,said polymerizable material comprising atleast one first monomer and at least one second monomer, said firstmonomer being a dimethacrylate of the following structure: ##STR12##where R₁ and R₂ may be the same or different and are cyclohexyl orphenyl groups which may be substituted or unsubstituted; and R₃ is analiphatic, cycloaliphatic or aromatic group having 6 to 15 carbon atoms,said second monomer being a diluent selected from the group consistingof di- and trimethacrylates having from 10 to 18 carbon atoms, saiddiluent further being selected from the group consisting of alkyleneglycol dimethacrylates, polyalkylene glycol dimethacrylates andalkanetriol trimethacrylates, said at least one first monomerconstituting at least 20% by weight of said polymerizable material, saidat least second monomer constituting at least 10% by weight of saidpolymerizable material, and the weight ratio of said filler to saidpolymerizable material being from about 1.5:1 to about 8.5:1.
 7. Acomposite restorative material according to claim 6, wherein saidpolymerizable material comprises from about 70% to about 80% by weightof said first monomer and about 20% to about 30% of said second monomerand the weight ratio of said filler to said polymerizable material isfrom about 4:1 to 6:1.
 8. A composite restorative material according toclaim 6, wherein both R₁ and R₂ of the dimethacrylate are unsubstitutedphenyl and R₃ is hexamethylene or a dicyclohexyl methane group of theformula: ##STR13##
 9. A composite restorative material according toclaim 6 wherein the weight ration of said filler to said polymerizablematerial is from about 1.5:1 to about 6.5:1.
 10. A composite restorativematerial according to claim 9 wherein said polymerizable materialfurther comprises at least one third monomer selected from the groupconsisting of 2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane,2,2-bis[4'(2"-methacroylethoxy)phenyl]propane,2-methacroylethyl-3-methacroyl-2-hydroxypropyl tetrahydrophthalate,2-methacroylethyl-3-methacroyl-2-hydroxypropyl hexahydrophthalate and2,2-bis(4'-methacroylphenyl)propane, the weight ratio of said firstmonomer to said third monomer being from about 3:5 to 5:3.
 11. A dentalmaterial according to claim 1 comprising a composite restorativematerial comprising glass or ceramic filler and polymerizablematerial,said polymerizable material comprising at least one firstmonomer and at least one second monomer, said first monomer being adimethacrylate of the following structure: ##STR14## where R₁ and R₂ maybe the same or different and are cyclohexyl or phenyl groups which maybe substituted or unsubstituted; and R₃ is an aliphatic, cycloaliphaticor aromatic group having 6 to 16 carbon atoms, said second monomer beinga diluent selected from the group consisting of di- and trimethacrylateshaving 10 to 18 carbon atoms, said diluent further being selected fromthe group consisting of alkylene glycol dimethacrylate, polyalkyleneglycol dimethacrylates and alkanetriol trimethacrylates, said at leastone first monomer constituting at least 20% by weight of saidpolymerizable material, said at least second monomer constituting atleast 10% by weight of said polymerizable material, and the weight ratioof said filler to said polymerizable material being from about 1.5:1 to8.5:1.